Obesity is an underlying risk factor for atherosclerosis and obesity-associated metabolic disorders. Inflammation has been linked as a key to both these processes. We seek to understand the role of T cells, of the adaptive immune system in these inflammatory processes. With respect to atherosclerosis, activated T cells have been found in human atherosclerotic plaques. We plan to evaluate the role of T cell activation in both adipose tissue and arterial wall inflammation by interfering with their activation by inhibiting tw distinct pathways of T cell co-stimulation. T cells are activated in a two-step process, initially involving T cell receptor- antigen recognition, and then activation of the CD80/86-CD28 pathway. Other co-stimulatory pathways that may be synergistic include the CD40-CD40L pathway. T cell activation is highly dependent on the co- stimulatory actions of these pathways. The CD80/86-CD28 pathway can be inhibited by CTLA-4 Ig, or abatacept, an FDA- approved biologic agent. The CD40-CD40L pathway can be inhibited by a neutralizing antibody to CD40 ligand (CD40L). Although blocking the CD40/CD40L pathway with an anti-CD40L antibody has been shown to ameliorate atherosclerosis, the effects of CTLA-4 Ig alone and in conjunction with anti- CD40L antibody on atherosclerosis have not been studied. Since the combination of CTLA-4 Ig and anti- CD40L antibody is a validated method of inducing tolerance in adaptive immune responses, it is important to test this combination in the setting of obesity-associated inflammation and atherosclerosis. The goal of this proposal is to evaluate the effects of these agents alone and in combination in the development of adipose tissue inflammation and atherosclerosis in mice. We plan on using LDL receptor knockout (Ldlr-/-) mice on the C57BL/6 background. These mice are susceptible to adipose tissue inflammation, insulin resistance and atherosclerotic lesion development when placed on a diet that resembles the typical Western diet that is high in saturated fat and cholesterol. In addition, we plan to evaluate the effects of fatty acids and HDL on T cell proliferation in vitro, which can lead to identification of mechanisms of adaptive immune response modulation by these molecules. Also, our preliminary in vitro data suggest a unique property of pre-adipocytes to develop molecules required for professional antigen presentation. We will expand these studies to confirm and identify the significance of this finding. Elucidating important pathways and agents that can mitigate the development of adipose tissue inflammation, insulin resistance and atherosclerosis may lead to further interventions for these conditions in humans. These projects will be part of a structured mentored career development program that will culminate in my becoming an independent investigator as a physician-scientist. My mentor and co- mentors have developed a plan to ensure that I attain my goals within the specified time frame of this opportunity. The research environment at the University of Washington is excellent for a budding physician- scientist, and I plan on taking absolute advantage of the resources available. (End of Abstract)